The present invention related to a fixing structure for safety helmet fastening strap, including a frame body mounted under a bottom of a helmet shell. The frame body has multiple fixing seats, which are securely connected with the frame body. The helmet shell, the frame body and the fixing seats are bonded with a foam material filler to together form an integrated body. The fixing seats can bear the extrusion force of the injection molded foam material without deflection or displacement.
A conventional safety helmet, such as a bicycle safety helmet or a horse-riding safety helmet, has a plastic shell and a foam material enclosed in the plastic shell. The plastic shell is airtight held in a vacuum mold and the foam material is injected into the vacuum mold to fill into the shell. Then, through a heating process, the plastic shell encloses the foam material to form the safety helmet. The conventional safety helmet is equipped with a fastening strap for fixing the safety helmet on a user's head. According to the foresaid safety helmet, the buckle ring has a projecting edge, a pinhole and a strap exit. After the buckle ring is placed into a mold, a foam material is injected into the mold to fill into the plastic shell of the safety helmet. At this time, the buckle ring is integrally bonded with the foam material. A stopper pin is transversely passed through the fastening strap and then the fastening strap is pulled out from the exit with the stopper pin engaged in the pinhole. The hidden buckle ring will not directly protrude from the bottom of the safety helmet as a conventional lug-type buckle ring. Therefore, the buckle ring is not likely to break off or abrade a wearer's face.
It is difficult to manufacture the above safety helmet. This is because before the foam material is injected, the plastic shell is separated from the buckle ring. Therefore, it is hard to retain the buckle ring in a set position in the mold. In general, a temporary fixing means is used to retain the buckle ring in the set position. However, the temporary fixing means is unreliable. When injecting the foam material into the mold, the extrusion force of the injected foam material often makes the buckle ring displace or deflect from its true position. As a result, after the shell and the buckle ring are bonded with the foam material to form the safety helmet, the safety helmet may have defects. The fastening strap may fail to connect with the buckle ring smoothly. Consequently, a wearer may feel uncomfortable when wearing such defective safety helmet or even can hardly wear such safety helmet stably.
In some cases, after the plastic shell and buckle ring are placed into the mold, a fixing mechanism or a clamping means is used to firmly retain the buckle ring in a set position without interfering with or obstructing the foam material injection molding process. Under such circumstance, the buckle ring is able to bear the extrusion force of the injected foam material. However, such arrangement leads to increased mold design cost and manufacturing cost.
There is another important topic in this field to consider. The buckle rings are independently bonded with the foam material. Therefore, an individual buckle ring is likely to disconnect from the foam material under sudden external force. That is, the buckle rings bonded with the foam material cannot share the external force to distribute the external force to the respective buckle rings.
FIG. 1 is a perspective view of another type of conventional safety helmet, showing how the fastening strap is assembled with the shell of the safety helmet. The plastic shell 70 is bonded with the foam material filler 80 with some holes 75 reserved. In practice, a fastening strap 90 is conducted through each hole 75 by an operator to pass through a buckle head 91. Then a tail end section 92 of the fastening strap 90 is sewn to loop the buckle head 91. Then the fastening strap 90 is pulled to engage the buckle head 91 in the hole 75. According to the above arrangement, the fastening straps 90 are passed through the foam material filler 80 and the plastic shell 70 with the buckle heads 91 engaged in the holes 75 formed through both the foam material filler 80 and the plastic shell 70. Therefore, the buckle heads 91 have sufficient load capability to bear the sudden external force.
However, as known by those skilled in this field, there are still some shortcomings existing in the manufacturing process of such structure. For example, the sewing operation is performed after the tail end section 92 of the fastening strap 90 is passed through the hole 75 and the buckle head 91. Therefore, it is necessary to place the entire safety helmet on a sewing table for the sewing operation. In this case, the safety helmet often obstructs the sewing operation and leads to troubles in the sewing operation or even danger of sewing workers. As a result, the tail end section 92 of the fastening strap 90 is often sewn with defects. Moreover, according to the above arrangement, when a wearer wears the safety helmet, the fastening strap 90 often abrades the face of the wearer. Also, the buckle heads 91 are exposed to outer side of the safety helmet. This deteriorates the appearance of the safety helmet.
Therefore, the following should be taken into consideration when designing the arrangement of the fastening strap and the safety helmet shell as well as the foam material filler:    1. The fastening strap fixing seats or the buckle rings should be securely fixed in the set positions without using any other additional fixing mechanism or clamping means to bear the extrusion force of the injection molded foam material without deflection or displacement.    2. The fastening strap should be fixed with the plastic shell and the foam material filler without affecting the appearance of the safety helmet or abrading the face of a wearer. Also, the sewing operation should be easy to perform.    3. All the fixing seats or the buckle rings should be securely connected with the plastic shell and bonded with the foam material filler to have better load capability. In this case, when an external force is suddenly applied to any of the fixing seats or buckle rings, the fixing seats or buckle rings can together bear the external force without breakage or detachment of any individual fixing seat or buckle ring as in the prior art.